30. Mammalian development

Question 1

What is considered day 0?

Answer 1

Fertilisation

Question 2

What happens at day 1?

Answer 2

First cleavage

Question 3

What happens at day 2?

Answer 3

2 cell stage then 4 cell stage

Question 4

What happens from days 3-4?

Answer 4

8 cell stage

Question 5

What happens at day 4?

Answer 5

Compacted morula

Question 6

What is formed at day 5?

Answer 6

Early blastocyte

Question 7

What is formed at day 6-7?

Answer 7

Late stage blastocyte (hatching)

Question 8

What happens at day 8-9?

Answer 8

Implantation of the blastocyte

Question 9

Why is there no yolk in mammal eggs?

Answer 9

Because all the nutrients the embryo requires are provided by the mother

Question 10

What does the first cleavage produce?

Answer 10

Produces blastomeres that are developmentally equivalent (holoblastic cleavage)

Question 11

What directions are the first and second cleavage?

Answer 11

First cleavage is a vertical cleavage

Second cleavage is one vertical and one horizontal

Question 12

Why do cells become smaller with each division?

Answer 12

For the restoration of the nuclear to cytoplasm ratio

Question 13

What happens with the activation of the embryo genome?

Answer 13

• Destruction of pre-stored mRNA

- But pre-stored proteins may continue to function and regulate development for some time

Question 14

What is cadherin?

Answer 14

A calcium dependent cell adhesion molecule

Question 15

What does cadherin do?

Answer 15

Mediates adhesion between blastomeres

- Cell outlines coalesce to form a morula

Question 16

What does the cleavage of blastomeres result in?

Answer 16

Some cells enclosed within the inner compartment of the morula

Question 17

What is cavitation?

Answer 17

What fluid begins to accumulate between blastomeres

Question 18

What does cavitation result in the formation of?

Answer 18

A blastocoel

Question 19

What is the outer layer of cells in the blastomeres?

Answer 19

The trophoblast/trophectoderm

Question 20

What does the trophectoderm give rise to?

Answer 20

The placenta

Question 21

What are the inner cells of the blastulation known as?

Answer 21

The inner cell mass

Question 22

What does the inner cell mass give rise to?

Answer 22

The embryo

Question 23

What is the purpose of the zona?

Answer 23

• The zona prevents cell-cell contact of the embryo and the oviduct wall so that there is no premature hatching
• Premature hatching causes a tubal pregnancy

Question 24

What happens during zona hatching?

Answer 24

• Hatching occurs in the uterus just before implantation

- Blastocyst secretes proteases that weaken the zona so that it implants to the uterine epithelium

Question 25

What are the changes in physiology of the embryo during the preimplantation period?

Answer 25

Embryo switches to using glucose rather than pyruvate

Question 26

How does the zygote generate energy?

Answer 26

Generates energy from low levels of oxidation of pyruvate and/or lactate with aspartate (and other amino acids).

Question 27

What does the blastocysts generate energy from?

Answer 27

Both aerobic glycolysis and the oxidation of glucose

Question 28

What is the morula defined as?

Answer 28

Once an embryo has compacted and formed tight junctions between blastomeres, the embryos is known as a morula

Question 29

How is the zona digested during zona hatching?

Answer 29

• Apical proteases (and uterine proteases) digest the glycoprotein zona pellucida
• The hatched blastocyst is free to implant into the endometrium of the uterus

Question 30

What does Na/K ATPase activity on the basolateral membrane result in?

Answer 30

An ionic gradient is formed and water flows into the embryo through aquaporins

Question 31

What are the exchanges during Na/K ATPase activity?

Answer 31

3 Na go in and 2K go out, water goes in

Question 32

What are the three phases of implantation?

Answer 32

Apposition, attachment and invasion

Question 33

What happens in the attachment phase?

Answer 33

• Loss of zona and glycocalyx

- Vascular changes

Question 34

What cells directly contact the uterus during attachment?

Answer 34

• Trophoblast directly contacts uterine epithelium

- Trophoblast cells start to penetrate epithelium

Question 35

What happens after the adhesion phase of embryo implantation?

Answer 35

• Trophoblast cells penetrate uterine epithelium, decidua and up to a third of myometrium
• Target maternal blood vessels and degrade them to provide adequate blood supply to growing foetus and placenta